The objective of this research is to develop an animal model for human clinical amnesia by investigating the exact nature of severe mnemonic impairments already found to exist in six rhesus macaques which one year ago sustained bilateral removals of the limbic system (hippocampus and amygdala) or rostral inferior temporal lobe (area T E). The monkeys will be given five tests to determine: 1) whether the animal model follows empirical findings in clinical literature, 2) whether the animals' deficits involve memory acquisition, memory maintenance, or memory retrieval and 3) whether the animals' deficits can be partially attenuated. Three groups of rhesus macaques have been or will be trained to criterion on a trial-unique visual delayed (10 sec) non-match-to-sample task. One group (N equals 3) has sustained bilateral removals of limbic structures and one group (N equals 3) has sustained bilateral removals of rostral inferior temporal lobe. Post-operatively both groups are severely impaired on the basic memory task; however, Limbic animals, but not the T E animals are able to distinguish "familiar" from novel stimuli, a finding which parallels data collected in Korsakoff amnesics. All three groups of animals will be given four tests which will measure the accuracy of memory as a function of (a) increased stimulus exposure time (b) enhanced stimulus contextual cues (c) massed vs distributed practice (d) partial stimulus cues during retrieval tests. A final concurrent visual discrimination test will be given to measure general learning and memory mechanisms. Finally, the lesions will be histologically verified.